Our immunocytochemical studies of the developmental expression of calretinin (CR) continue with observations in the forebrain of the formalin fixed c57BL/6J mouse embryo using a specific antiserum. A large prominant CR-immunoreactive area was observed in the forebrain region during the embryonic periods E11-E17. This region has been tentatively identified as the bed nucleus of the stria terminalis (BST). There appears to be a close correlation between the appearance of CR and the period of neurogenesis and migration of the neuronal cells of the BST. The early appearance of CR leads us to speculate that this protein plays a role in the neurogenesis and migration of the neurons within the BST.